Earth-Size Storm and Fireballs Shake Jupiter as a Comet Dies

By MALCOLM W. BROWNE

Published: July 19, 1994

Correction Appended

A continuing bombardment by fragments of the dying Comet Shoemaker-Levy 9 ignited flashes on Jupiter yesterday that outshone the giant planet itself, sending up blazing fireballs and churning the Jovian atmosphere into dark storms, one of them as large as Earth.

The most spectacular of yesterday's impacts was that of Fragment G, which was believed to be the largest of the 21 comet remnants expected to hit Jupiter by Friday. The impact, at 3:28 A.M. Eastern time, produced a flash and a fireball so dazzlingly bright that sensitive instruments on large telescopes were unable to measure its intensity. Briefly the flash exceeded the normal brightness of the entire planet.

The fireball rose above the Jovian horizon in view of terrestrial telescopes and left a darkened region of violently churning gases equal in size to Jupiter's semipermanent Great Red Spot, a more or less circular region with about the same diameter as that of Earth.

The impact of Fragment G was so violent, in fact, that many amateur astronomers were able to see it using telescopes no more powerful than those with light-collecting mirrors four inches in diameter, said Dr. Brian G. Marsden, director of the Central Bureau for Astronomical Telegrams at the Smithsonian Astrophysical Observatory in Cambridge, Mass.

The comet ventured too close to Jupiter's mighty gravitational pull two years ago and was pulled apart into a score of large fragments and thousands of small ones. As each fragment hits Jupiter's dense atmosphere, it is stopped as if it had hit a brick wall. In an instant, its initial speed of 130,000 miles per hour is reduced to zero, and practically all of its gigantic kinetic energy is converted to heat -- so much heat that a titanic explosion results. In the case of each of the largest fragments, this is equivalent to 250 million megatons of TNT. (The largest hydrogen bomb ever detonated produced a blast equivalent to about 58 megatons.)

The cometary impacts have all occurred on the back side of Jupiter, not directly visible from Earth. Astronomers must be content with observing the impact sites after Jupiter's rotation swings them into view. But the staggering power of these blasts can be gauged from the fact that the fireballs they produce actually peak above Jupiter's horizon and can be seen through Earth telescopes.

Since the first impact on Saturday afternoon, the flashes and fireballs of successive impacts have subsided within minutes. But as the days pass, the dark blemishes left by most of them continue to return to view each time Jupiter completes a new revolution, every nine hours and 56 minutes. Spots marking the wounds caused by Fragments A, C, E and G are scattered in a line across Jupiter's southern hemisphere and have scarcely faded since they first appeared.

Yesterday afternoon, another giant cometary chunk, Fragment H, hit with a blast of light that observers at the French-Swedish-Spanish Nordic Optical Telescope Team at La Palma, Canary Islands, described as "fantastic."

So far astronomers have had little time to assess the mountain of data their instruments are collecting. Many observers yesterday had gone without sleep for two days or more, often fighting inclement weather to continue their work. Fighting the Cold and Snow

Nowhere were conditions more daunting than at the South Pole, the only place on Earth where an astronomical telescope can keep Jupiter in view 24 hours a day because of the continuous nighttime darkness of the Southern Hemisphere winter. The South Pole Infrared Explorer, a 24-inch-diameter telescope, has produced some of the most important images of the comet fragment impacts, but the telescope's operators have been enduring an ordeal.

Dr. Nguyen Trong Hien of the University of Chicago reported that the temperature yesterday was colder than minus 80 degrees Fahrenheit and that a wind of 25 m.p.h. was blowing snow directly into the open snout of the telescope. But just before the impact of Fragment E -- one of the largest in the series -- the wind died, Dr. Hien's team cleaned out the snow, and he managed to record a 15-minute sequence of images. At the peak of the sequence, the South Pole observatory saw a fireball blaze up and persist for 15 minutes, much longer than those produced by Fragments A or C.

"The new data will provide us an opportunity to study the impact evolution and will probably allow us to say something definite about the chemical composition of Jupiter's atmosphere," Dr. Hien said in an interview conducted by electronic mail.

Somewhat less dramatic but nevertheless troublesome weather has plagued other observatories in many parts of the world.

The array of major international observatories on Mauna Kea mountain in Hawaii, which, along with an observatory complex in northern Chile, is one of the two most important in the world, has had to contend with fog and rain. But Dr. Imke de Pater, one of the team leaders at the Keck Observatory on Mauna Kea, said that her group had good luck at a critical moment yesterday. Just in Time

Correction: July 20, 1994, Wednesday A front-page article yesterday about the fragments of Comet Shoemaker-Levy 9 that struck Jupiter misstated the size of the largest nuclear explosion ever set off on Earth. It was 57 megatons, not 5.